of copper formed. The absorption of oxygen is rapid and complete. We use the same solution for about two weeks, making about twenty analyses with each filling.
results obtained by the students in different classes and ditferent years.
PROCEDURE
a. Filling the Bwrct with Dislilkd Wa&.--See that the buret is open, through the stopcock, to the air. Half fill the buret and leveling tube with distilled water. Now connect the buret with the, pipet through the stopcock. Lower the leveling tube slowly until the air is withdrawn from the pipet and the column of liquid stands in the capillary tube on a level with the horizontal portion of the pipet. Mart this point and always bring the liquid in the pipet ba& to this point. Next shut off the pipet by means of the stopcock and open the buret to the air. Raise the leveling tube and force out the air in the buret until the surface of the water in the buret is at the zero mark and thesurfaces of the liquids in the two tubes are level. b. Tnkinz the Sample of Air.-With the surfaces of the water in the leveling tube and buret level, open the stopcock to the air and gradually lower the leveling tube. This lets the air enter the buret. Continue lowering the leveling tube until the surfaces of the water in the tubes are level at the 100-ml. mark. To make the reading more accurate, place the two tubes in contact with the water levels the same, comparing the undersurfaces of the menisci. Now close the stopcock. Repeat reading and assure younelf that you have exadly 100 ml. of air under atmospheric pressure. c. Transference of Sample of Air to Pipet.-See that the pipet is full of liquid, the surface in the vertical capillary tube being even with the horizontal portion of the capillary tube of the pipet. By means of the stopcock, connect the pipet with the buret. Raise the leveling tube slowly and force the air sample into the pipet. It is necessary to keep the surface of the water in the leveling tube a few inches above the surface in the buret. When a l l the air has been transferred to the pipet, allow it to stand in contact with the copper for about five minutes. Then return the air to the buret by lowering the leveling tube, level the liquid surfaces, and read the volume of the air in the buret. Record the reading. Now return the air to the pipet. Allow it to remain in contact with the copper and salutim about five minutes, then return it to the buret. Level the water surfaces and read the volume of air remaining. Repeat this process three or more times until the last two readings of the residual gas volume are the same. Record this as your final reading. Connect the buret with the atmosphere, raise the leveling tube, and remove all the residual gas from the buret and the pipet. Introduce a new sample of air into the buret and measure it in the manner desnibed above. Transfer it to the pipet three successive times or until the volume of the residual gas is constant and take the 6nal constant r e a d i i as described. Record this value. Take a third samnle of air and treat it in the manner iust described. heavera age of the values for the three differentlamplev of air g i v e the volume of the residual gas and this deducted from 100 ml. gives the volume of orggen in 100 ml. of air. Calculate the percentage of oxygen in air. ~~
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RESULTS OBTAINED BY STUDENTS
In the following table are presented a few of the
VII
VIII
Each Roman figure represents the experiments of one pair of students and there are listed in each case three analyses, indicating the exercise was done in triplicate. These are typical student results, as obtained by class after class. The time required for the exercise is one laboratory period of two hours, the students working in pairs, because of the necessity imposed by limited equipment. No etfort is made to correct the gas volumes for the vapor pressure of water at room temperature, since with us this exercise is performed before the gas laws have been considered. The correction would be smaller than the manipulative ability of the students a t this stage justifies.
DEATH OF MISS OCTAVIA CHAPIN We regret to have to announce the death, on May Xth, of Miss Octavia Chapiu. Miss Chapin was an instructor in the high school a t Malden, Massachusetts, and had long been an active member and secretary of the New England Association of Chemistry Teachers. She abstracted the Report of that association for the JOURNAL.
